The frame of a bicycle light and capable of maintaining a certain strength is generally made of a tube structure. When a front wheel part and a rear wheel part are coupled, a tube or a rod inserted into the interior of the above mentioned coupling tube is coupled into either end of a separated portion and is fixed using a pin or the like so that it cannot be separated. In this case, it is possible to fix in order that the couple portion may not be loosened; however the tube or the rod is inserted into the connection tube connecting the front wheel part and the rear wheel part should have a diameter smaller than that of the coupling tube for the sake of an insertion and separation, so a certain rattle and loosening might occur between the front wheel part and the rear wheel part due to a gap formed owing to the difference in the diameters after they are coupled, and it is hard to have a desired safety after long time operation.